This disclosure generally relates to test equipment for photovoltaic cells and, more particularly, relates to solar simulator systems used in testing of photovoltaic cells.
Photovoltaic cells (solar cells) have been used for many years to generate electrical energy from sunlight. Solar panels, which typically include many individual cells, have been deployed in space and terrestrial applications. Terrestrial photovoltaic cells are quickly becoming a viable product and, therefore, techniques, equipment, and technologies related to the testing of terrestrial cells in a quick and economical manner are in demand.
Terrestrial photovoltaic cells may be exposed to “multiple” sun sources using mirrors, reflectors, and/or lenses that concentrate sunlight into a smaller area, which results in higher radiation energy per square unit of area. Such concentration is desirable to generate higher current per cell. Accordingly, test equipment and technologies for terrestrial photovoltaic cells are often designed to test cells using light that emulates the solar energy equivalent to 500-5000 individual suns. This high level of solar energy may be necessary to accurately characterize the performance of the cells in the intended application.
Unlike photovoltaic cells designed for outer space applications, terrestrial photovoltaic cells can be exposed to sunlight that is “filtered” through different atmospheric and/or environmental conditions. Moreover, the altitude at which the cells will be deployed can influence the spectral (wavelength) characteristics of sunlight. Consequently, a solar simulator for testing photovoltaic cells should be configured to provide accurate spectral adjustability to simulate different types of sunlight conditions.
Solar simulator systems typically operate at the upper end of the lamp current range to obtain a target optical power density. The lamps are operated at a current to obtain the desired optical power density, and when the lamp dies or becomes unstable, the system operator changes out the lamp.
In many solar simulator designs, the exit beam size and therefore the optical power density at the illumination plane is constant and defined by the original design. Due to optical losses or test requirements that call for increased power density (at the possible expense of total illumination area), it is desired to be able to de-magnify the exit beam to provide higher power densities at the illumination plane. Presently, with at least one existing design, the power density cannot be changed without a significant redesign of many of the optical elements.
It would be desirable to provide means and methods for retrofitting known solar simulator systems to allow the exit beam to be changed in size and location without changing the other fundamental functions of the main optical elements.